 /* 1. 全局样式与重置 */
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
      font-family: 'PingFang SC', 'Microsoft YaHei', sans-serif;
    }
    
    :root {
      --primary-color: #3f51b5;
      --secondary-color: #2196f3;
      --accent-color: #ff5722;
      --light-color: #f5f7fa;
      --dark-color: #2c3e50;
      --text-color: #34495e;
      --border-radius: 8px;
      --shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
    }
    
    body {
      background-color: #f8f9fa;
      color: var(--text-color);
      line-height: 1.6;
      overflow-x: hidden;
    }
    
    a {
      text-decoration: none;
      color: var(--primary-color);
      transition: color 0.3s ease;
    }
    
    a:hover {
      color: var(--accent-color);
    }
    
    ul {
      list-style: none;
    }
    
    /* 2. 布局容器 */
    .page-container {
      max-width: 1440px;
      margin: 0 auto;
      padding: 0 20px;
      position: relative;
    }
    
    /* 3. 顶部导航区 */
    .main-header {
      background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
      color: white;
      padding: 15px 0;
      position: sticky;
      top: 0;
      z-index: 1000;
      box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
    }
    
    .primary-nav {
      display: flex;
      justify-content: space-between;
      align-items: center;
      max-width: 1200px;
      margin: 0 auto;
    }
    
    .primary-nav a {
      color: white;
      font-size: 16px;
      font-weight: 500;
      padding: 8px 16px;
      border-radius: var(--border-radius);
      transition: background-color 0.3s ease;
    }
    
    .primary-nav a:hover {
      background-color: rgba(255, 255, 255, 0.15);
    }
    
    .search-bar {
      display: flex;
      align-items: center;
    }
    
    .search-bar input {
      padding: 10px 15px;
      border: none;
      border-radius: var(--border-radius) 0 0 var(--border-radius);
      font-size: 14px;
      min-width: 280px;
      outline: none;
    }
    
    .search-bar button {
      background-color: var(--accent-color);
      color: white;
      border: none;
      border-radius: 0 var(--border-radius) var(--border-radius) 0;
      padding: 10px 20px;
      cursor: pointer;
      transition: background-color 0.3s ease;
      font-weight: bold;
    }
    
    .search-bar button:hover {
      background-color: #e64a19;
    }
    
    /* 4. 主体内容区 - 三栏布局 */
    .main-content {
      display: grid;
      grid-template-columns: 250px 1fr 300px;
      gap: 30px;
      padding: 30px 0;
      min-height: calc(100vh - 400px);
    }
    
    /* 5. 左侧侧边栏 */
    .sidebar {
      background: white;
      border-radius: var(--border-radius);
      box-shadow: var(--shadow);
      padding: 20px;
      height: fit-content;
    }
    
    .category-menu li {
      padding: 14px 16px;
      border-radius: var(--border-radius);
      cursor: pointer;
      font-size: 15px;
      transition: all 0.3s ease;
      margin-bottom: 6px;
    }
    
    .category-menu li:hover {
      background-color: rgba(63, 81, 181, 0.1);
      color: var(--primary-color);
      font-weight: 500;
    }
    
    /* 6. 中间内容区 */
    .content-area {
      display: flex;
      flex-direction: column;
      gap: 30px;
    }
    
    .carousel {
      border-radius: var(--border-radius);
      overflow: hidden;
      box-shadow: var(--shadow);
      position: relative;
      height: 350px;
      background: linear-gradient(45deg, #1a237e, #3949ab);
      color: white;
      display: flex;
      flex-direction: column;
      justify-content: center;
      padding: 40px;
    }
    
    .carousel h1 {
      font-size: 3.2rem;
      margin-bottom: 15px;
      letter-spacing: 0.5px;
      text-shadow: 0 2px 4px rgba(0, 0, 0, 0.3);
    }
    
    .carousel p {
      font-size: 1.4rem;
      opacity: 0.9;
    }
    
    .recommendation-section {
      background: white;
      border-radius: var(--border-radius);
      padding: 25px;
      box-shadow: var(--shadow);
    }
    
    .recommendation-section h2 {
      color: var(--dark-color);
      font-size: 1.8rem;
      margin-bottom: 25px;
      padding-bottom: 15px;
      border-bottom: 2px solid rgba(63, 81, 181, 0.2);
    }
    
    .course-grid {
      display: grid;
      grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
      gap: 25px;
    }
    
    .course-card {
      background: white;
      border-radius: var(--border-radius);
      overflow: hidden;
      box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
      transition: transform 0.3s ease, box-shadow 0.3s ease;
    }
    
    .course-card:hover {
      transform: translateY(-8px);
      box-shadow: 0 10px 25px rgba(0, 0, 0, 0.12);
    }
    
    .course-card .card-header {
      height: 150px;
      background: linear-gradient(45deg, #3949ab, #00bcd4);
      position: relative;
      display: flex;
      align-items: center;
      justify-content: center;
      color: white;
      font-size: 1.6rem;
      text-align: center;
      font-weight: bold;
    }
    
    .course-card .card-content {
      padding: 20px;
    }
    
    .course-card h3 {
      font-size: 1.3rem;
      margin-bottom: 10px;
      color: var(--dark-color);
    }
    
    .course-card p {
      color: #7f8c8d;
      font-size: 0.95rem;
    }
    
    /* 7. 右侧用户功能区 */
    .user-panel {
      display: flex;
      flex-direction: column;
      gap: 25px;
    }
    
    .login-box, .user-profile {
      background: white;
      border-radius: var(--border-radius);
      box-shadow: var(--shadow);
      padding: 25px;
    }
    
    .login-box h3, .user-profile h3 {
      font-size: 1.4rem;
      margin-bottom: 20px;
      color: var(--dark-color);
    }
    
    .login-box input {
      width: 100%;
      padding: 12px 15px;
      margin-bottom: 15px;
      border: 1px solid #ddd;
      border-radius: var(--border-radius);
      font-size: 14px;
    }
    
    .login-box button {
      width: 100%;
      padding: 12px;
      background-color: var(--primary-color);
      color: white;
      border: none;
      border-radius: var(--border-radius);
      cursor: pointer;
      font-weight: 500;
      transition: background-color 0.3s ease;
    }
    
    .login-box button:hover {
      background-color: #303f9f;
    }
    
    .user-profile {
      text-align: center;
    }
    
    .user-profile .avatar {
      width: 100px;
      height: 100px;
      border-radius: 50%;
      background: linear-gradient(45deg, var(--primary-color), var(--secondary-color));
      margin: 0 auto 20px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 40px;
      color: white;
    }
    
    /* 8. 底部扩展内容区 */
    .additional-courses {
      background: white;
      border-radius: var(--border-radius);
      box-shadow: var(--shadow);
      padding: 30px;
      margin-bottom: 40px;
    }
    
    .additional-courses h2 {
      color: var(--dark-color);
      font-size: 1.8rem;
      margin-bottom: 25px;
    }
    
    .course-horizontal-scroll {
      display: grid;
      grid-auto-flow: column;
      gap: 20px;
      overflow-x: auto;
      padding-bottom: 10px;
      scrollbar-width: thin;
      scrollbar-color: var(--primary-color) transparent;
    }
    
    .course-horizontal-scroll::-webkit-scrollbar {
      height: 8px;
    }
    
    .course-horizontal-scroll::-webkit-scrollbar-thumb {
      background-color: var(--primary-color);
      border-radius: 4px;
    }
    
    .course-horizontal-scroll .course-card {
      min-width: 280px;
      margin-bottom: 5px;
    }
    
    /* 9. 响应式设计 */
    @media (max-width: 1200px) {
      .main-content {
        grid-template-columns: 220px 1fr;
      }
      
      .user-panel {
        grid-column: 1 / span 2;
        display: grid;
        grid-template-columns: 1fr 1fr;
        gap: 20px;
      }
    }
    
    @media (max-width: 900px) {
      .primary-nav {
        flex-direction: column;
        gap: 15px;
      }
      
      .search-bar input {
        min-width: 220px;
      }
      
      .main-content {
        grid-template-columns: 1fr;
      }
      
      .user-panel {
        grid-column: auto;
        display: flex;
        flex-direction: column;
      }
      
      .course-grid {
        grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
      }
      
      .carousel {
        height: 280px;
        padding: 30px;
      }
      
      .carousel h1 {
        font-size: 2.5rem;
      }
    }
    
    @media (max-width: 600px) {
      .course-grid {
        grid-template-columns: 1fr;
      }
      
      .search-bar input {
        min-width: 180px;
      }
      
      .carousel h1 {
        font-size: 2rem;
      }
    }
    
    /* 10. 动画效果 */
    @keyframes fadeIn {
      from { opacity: 0; transform: translateY(20px); }
      to { opacity: 1; transform: translateY(0); }
    }
    
    .course-card {
      animation: fadeIn 0.5s ease backwards;
    }
    
    .course-card:nth-child(2) { animation-delay: 0.1s; }
    .course-card:nth-child(3) { animation-delay: 0.2s; }
    .course-card:nth-child(4) { animation-delay: 0.3s; }